Two-way transmission with repeaters



J. MILLS. TWO-WAY TRANSMISSION WITH REPEATE APPLICATION FILED SEPT- 6, I919.

Patented Nov. 7, 1922.

2 SHEETSSHEET I.

EL Iv I J. MILLS. TWO-WAY TRANSMISSION WITH REPEATERS. APPLICATION FILED SEPT. 6. 1919.

Patented Nov. 7, 1922,

2 SHEETS-SHEET 2.

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Patented JOHN MILLS, OF WYOMING, NEW JERSEY, ASSIIIG'NOIIR' TO WESTERN ELECTRIC COM- PATENT FFICE.

PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TWO-WAY TRANSMISSIQN WITH REPEATERS.

Application filed September 6, 1919. Serial No. 322,154.

To all whom it may concern:

Be it known that I, JOHN MILLS, a citizen of the United States, residing at Wyoming, in the county of Essex, State of New Jersey, have invented certain new and useful Improvements in Two-Way Transmissions with Repeaters, of which the following is a full, clear, concise, and exact descriptiom This invention relates to repeater circuits and more particularly to telephone lines in which are employed one or more repeaters for carrying currents in one direction and one or more other repeaters for carrying currents in the opposite directions.

(Jircuits of the above type frequently rely upon a condition of balance between the real line and an artificial network of impedances to prevent currents which are transmitted in B one direction from being transmitted back to the sending end through the oppositely directed repeater. or repeaters. Due to changing Weather conditions or other causes,

it is sometimes difiicult or impracticable to maintain this condition of balance, and as a result there are heard echoes which lag slightly behind the original voice vibrations.

It is the object of this invention to pro vide means for preventing the echo currents above described.

In the forms of the invention disclosed herein a pair of switches are introduced in the two wires of the portion of the circuit which transmits currents only inthe direction toward the sending station. These switches are arranged to be operated by a voice operated relay associated with the portion of the circuit transmitting currents awa from the sending station.

Tl ie invention therefore contemplates the provision of means, such as a line balancing network, designed to prevent circulating currents in repeater circuits, and additional means to prevent their flow in case the first means is inadequate. Conversely if the additional means should become inoperative, the circuit is not rendered inoperatlve since as above stated the relay contacts are normally closed. j q

The invention will be more fully understood from the following detailed description and claims taken in connection with the accompanying drawings, in which Fig. 1 is a circuit diagram showing the invention ap- View showing the invention applied to a four-wire line.-

By a two-wire line is meant one in which the talking currents in both directions are earned over the-same pair of wires for the greater portion of the distance. By a fourw1re line is meant one in which the talking currents 1n one direction for the greater portion of the distance are carried over a difierent pair of wires from the currents in the other direction.

Referring to Fig. 1, the subscribers stat1on A is connected through four two-way repeater stations to the subscribers station ]Each repeater station comprises two oppositely directed repeaters R which may be of the thermionic type as show in Fig. 2. The transformers H which connect the repeaters to the intervenin line sections L, are

also shown in detail in ig. 2. Connected to each transformer H is a network of impedances N designed to balance the impedance of the line section L connected thereto, and substantially prevent the signal currents going in one direction through one of the repeaters from flowing back through the other repeater at the same station.

Referring in detail to Fig. 2 which represents a circuit which may be used at repeater station 2, the line conductors 3 and 4 of one line section L terminate in an artificial network or balancing line 5 which is designed to have an impedance equivalent to that of the line section. Between the line conductors and the balancing network are inserted the four equal windings 6, 7, 8 and 9 of the repeating coil 10. Between the point of junction of windings 6 and 7 and the point of junction of windings 8 and 9 is inserted a bridge comprising resistances 11 and 12 and capacities 13 and 14, as shown. The middle points of the capacity bridge and the resistance bridge thus formed are connected together and to the cathode element 15 of the vacuum tube repeater 16, the

by means of the battery 20'. The output circuit of repeater 16 is connected through the condensers 20 to the primary windings 21 of the transformer 22, whose secondary windings 23, 24, 25 and 26 are connected in series with the line conductors 27 and 28 of another line section which terminates in its balancing network 29. Repeater 16 is thus arranged to repeat into line conductors 27 and 28 amplified currents similar to'those arriving over linev conductors 3 and 4. In a similar manner, repeater 30 by means of windings 31 and 32, is arranged to repeat into line conductors 3 and 4 telephonic or other currents arriving over line conductors 27 and 28.

' The circuit of Fig. 1 as thus far described is identical in arrangement and mode of operation with the circuit of Fig. 1 of Kendall Patent No. 1,216,136, dated February 13, 1917.

In carrying out the object of the present invention a pair'of normally closed switches 33 is placed in the output circuit of repeater 30. These switches may form the armatures or may beconnected to the armature of a voice operated relay 34, which is inductively related to the input circuit of repeater 16 by a transformer 35. When voice currents come in to the repeater set from the line 3, 4, the electromagnet of relay 34 is energized and the output circuit of repeater 30 is opened. This prevents any portion of the talking current from flowing back on to line 3, 4 even if there is a condition of unbalance at a subsequent repeater station.

It will be noted that the return current whose transmission beyond the relay contacts, 33, is to be prevented, will arrive at these contacts later than the original transmission through transformer 35 by a time interval equal to twice the time required for propagation of a current through the line' from the repeater circuit shown in Fig. 2' to the repeater circuit at that subsequent repeater station where the impedance unbalance is such that reflection occurs. For this reason it is possible to utilize mechanical relays in whose operation there is inevitably a time lag between the electrical cause and the completed mechanical efl'ect. Instead of such time lag introducing a difliculty of operation as is true of many applications of voice-operated relays, it is advantageously utilized in this invention.

- Referring to Fig. 1 a similar relay 36 comprising switches 37 is placed at repeater station 3, and is arranged to be operated by voice currents coming from subscribers station B. This relay when operated opens the circuit of the repeater normally carrying currents in the direction of station B, thereby preventing circulating currents from repeater stations to the left of repeater station 3 from passing through repeater station 3, and hence from reaching station B or being returned to station A as echoes.

Referring to Fig. 3, the telephone substation 40 is connected through line section 41 and the transformer comprising windings 6, 7, 8, 9, 31 and 32 to the pair of line wires 42 adapted to transmit only in a direction away from substation 40 and to a similar pair of line wires 43 adapted to transmit toward substation 40. Network 44 is designed to balance the impedance of line 41. The line wires 42 have interposed therein a series of one way repeaters R R and R which may be of the thermionic type. Associated with line wires 43 is a similar series of repeaters R R and R which are directed oppositely to those in line 42. It will be understood that line sections of considerable length intervene between the various repeaters.

Substation 45 is connected tothe line wires 42- and 43 and balancing network 46 by means of a transformer 22 similar to that shown in Fig. 2.

At a desired point in one of the line wires 42 is placed the primary of a transformer 47, the secondary circuit of which includes the relay 48. This relay is similar to relays 34 and 36 and when voice currents from substation 40 are sent out on the line 42,the relay operates to open line 43 by means of switches 49 and thus prevents currents from circulating back to the receiving station as echoes.

A similar relay 50 having normally closed contacts 51 is provided to prevent echo currents when substation 45 is sending.

While the invention has been shown applied to two forms of telephone circuits it is to be understood that it is not limited to the specific forms shown, but is capable of general application within the scope and spirit of the appended claims.

What is claimed is:

1. A two-way signaling system comprisingpaths adapted to transmit in opposite directlons, means tending to prevent circu-' .in the other of said paths, a normally closed contact in one of said paths, and a voice operated relay associated with the other of saidpaths and adapted when energized by voice currents to open said contact. v

3. In combination two line sections, two unidirectional oppositely directed paths between said line sections, impedance elements substantially balancing the impedances of said line sections respectively, said unidirectional paths being so related to said line sections and to said balancing impedances that only a relatively small amount of current traversing one of said paths is fed back through the other of said paths, and means of said repeaters for opening the circuit of another of said repeaters Without disturbing transmission through said first repeater.

5. In a telephone system, a sending station, an outgoing vpath for signals, a return path for a portion of said outgoing path, connections permitting circulating currents in said return path, and means operated by signals in said outgoing path for preventing the flow of said circulating currents to said sending station, said signal operated means having a time lag substantially equal to the time lag of said circulating currents.

In Witness whereof, I hereunto subscribe my name this 3rd day of. September A. D., 1919.

JOHN MILLS. 

